THF-15 SatellitePreliminary Design Review

Team Having Fun THF-15 SatelliteMatt Chapin1, Nick Wackel1, Olon Pierce1

The University of Alabama, Tuscaloosa, AL 35487

This report details a preliminary design proposal for repairing, on orbit, the Thermal Infrared Sensor onboard Landsat 8 to extend its mission design life. Landsat 8 is an American Earth observation satellite developed by NASA Goddard Space Flight Center and the United States Geological Survey. The purpose of this report is to present a feasible mission plan, projected risk, and projected cost for Preliminary Design Review.

I. Overview

Landsat 8 (Fig. 1) is an American Earth observation satellite launched on February 11, 2013. It is a collaboration between NASA and the United States Geological Survey (USGS) with the underlying goal of “monitoring, understanding, and managing the resources needed for human sustainment such as food, water and forests” [1]. Landsat 8 collects multispectral images of Earth’s land surface and Polar Regions. Instrumental in the collection of this data, the Thermal Infrared Sensor (TIRS) conducts thermal imaging of two long-wavelength infrared bands. TIRS was a late addition to Landsat 8 and thus had a relaxed design-life of three years. In order to extend the life of the Landsat 8 mission, NASA and USGS have developed a robot capable of removing and replacing the sensor and request TIRS be retrofitted on orbit.

Figure 1. Landsat 8 Satellite

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A. Mission Objective

The primary objective of the THF-15 satellite is to deliver the robot developed by NASA and USGS to Landsat 8 and ensure successful completion of the TIRS repair. THF-15’s mission will be considered a success if the following criteria are met:

1. THF-15 intercepts Landsat 8 on orbit without severely altering its orbital trajectory and causing structural or electronics damage.

2. THF-15 deploys the repair robot and installs the new TIRS on Landsat 8.3. THF-15 detaches from Landsat 8 and performs a maneuver to enter a parking orbit.

Secondary objectives could be potential consequences of the THF-15 satellite project. For example, successful completion of the primary objective will demonstrate lifespan-extension capabilities for the Landsat project. The Landsat 8 satellite has a lifespan of five to ten years and therefore will require an additional Thermal Infrared Sensor to remain fully operational for the remaining third of its lifespan.

B. Key Players

The Landsat Program is a joint operation between NASA and the USGS. NASA accounted for the mission systems development and launch segment, while the USGS provided the ground systems structure and currently conducts mission operations. For the past forty years, the Landsat Program has been continually capturing vital images of Earth’s surface. This multi-decade spanning archive of data has provided natural resource experts, hydrologists, urban planners, farmers, disaster responders, law enforcement agencies, and many other kinds of experts with important information that can only be acquired from space. One major reason behind the success of the Landsat Program is the continuity of images over its entire lifespan. Losing thermal band sensor capability would severely diminish this success and strike a blow to the scientific community and resulting economic benefit.

With the long-term future of the Landsat Program uncertain, Landsat 8’s lifespan must be extended. Typical new mission development takes five to six years which would result in a successor, Landsat 9, being operational no sooner than 2019. This results in a three year period, the entire lifespan of TIRS, where there would be limited mission capability.

The development, production, and operation of THF-15 would have a direct benefit to the economy. Each stage will create a significant amount of jobs and could lead to substantial advances in technology. With regards to the investment of congressional spending on this project, the economy could expect a 14% gain from each dollar spent.

C. Critical Systems Drivers

1. Performance

Performance is a critical systems driver because it characterizes the functionality of the THF-15 satellite throughout the completion of its primary objective. THF-15 will transport the NASA/USGS repair robot weighing 100 kilograms to Landsat 8. It must safely intercept Landsat 8 on orbit by performing a reverse thrust maneuver to slow its velocity. THF-15 must then securely attach to the satellite structure without affecting Landsat 8’s structural integrity. Complete autonomy is required of the repair robot during its retrofit of the TIRS. Additional fuel is necessary to disengage from Landsat 8 and enter a parking orbit with potential orbital transfer capabilities.

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2. Schedule

The existing TIRS on Landsat 8 will expire in early 2016. Launch of the THF-15 satellite must occur by the end of 2016 to minimize the interruption in Landsat observations. Traditionally, the baseline for minor satellite missions is an operational timeline of less than five years. THF-15 uses this model to estimate time budgets for each phase of the operational timeline. The Conceptual Development Phase will focus on securing government funding by conducting research and performing cost feasibility analysis. A Preliminary Design Review will take place, and upon approval, THF-15 will proceed to the Detailed Development Phase. This phase includes detailed mission design, technology development, and risk mitigation. With most of the necessary technology (i.e. the repair robot and spare TIRS) already developed by NASA and the USGS, THF-15 can reduce the amount of time spent in this phase. The project will then undergo a Critical Design Review, and pending approval, will enter Production and Deployment. This phase contains the manufacturing of the satellite, launch segment, and operational check once THF-15 reaches the target orbit. The THF-15 satellite will then be operated by the USGS until its retirement.

Table 1. THF-15 Operational Timeline

Phase Description Time Budget

Conceptual Development

MarketingResearch

2 months4 months

Detailed DevelopmentTech Development/Risk

MitigationDetailed Design

4 months 8 months

Production/DeploymentProduction

LaunchOps Check on Orbit

5 months1 month10 days

Operation USGS Control 5 years

Retirement Orbit Transfer 1 month

As shown above, THF-15 will have initial operating capability within two years. This fulfills the requirement of replacing the Thermal Infrared Sensor by the end of 2016.

3. Risk

Risk is a critical driver for the THF-15 satellite project. Design choices have been made to minimize risks and provide the greatest reliability possible. At this development phase, the majority of risk mitigation has occurred within the launch segment design. As THF-15 enters detailed development, more focus will be placed on risk studies as the satellite subsystems are developed.

4. Cost

The cost of the THF-15 satellite mission is determined as a function of physical parameters, orbit, complexity, and autonomy. Physical parameters of THF-15 are the mass and volume of the payload and bus, and will influence the launch vehicle selection. The primary objective includes intercepting Landsat 8, so Landsat 8 sets the orbit requirement. Since THF-15 is a minor satellite project, the level of bus autonomy will be limited to orbit and attitude control. However, the NASA/USGS repair robot will be

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entirely autonomous. Complexity will be discussed primarily in the detailed development phase. These costs will be separated in to two categories, recurring and non-recurring. Recurring costs for the THF-15 project will be predominantly operational costs. Non-recurring costs will include research, design, testing, manufacturing, and launching.

II. Mission Design

A. Launch Segment

The launch design for THF-15 is based on the target orbit and timing requirement of the primary objective. The launch window for a spacecraft intending to intercept another vehicle in orbit must be carefully planned to occur within the time that the target’s orbital plane intersects the launch site. Additionally, the time for a launch vehicle to reach a low earth orbit is in the range of seconds to minutes, leaving almost no room for error. To provide additional flexibility in launch time, THF-15 will be sent to a parking orbit. This will result in an increase of the launch window by up to several hours. A major disadvantage of using a parking orbit is requiring a launch vehicle that can stop and restart under zero-G conditions. This limits the launch vehicle to liquid fuel engines with restart capabilities.

B. Orbit

Landsat 8 occupies a low earth orbit with an eccentricity of 9.07e-5 kilometers, perigee of 708 kilometers, apogee of 710 kilometers, inclination of 98.23˚, and period of 98.83 minutes. It is classified as sun-synchronous (SSO) due to its altitude and inclination. Fig. 2. Demonstrates how the orbit of Landsat 8 allows it to cover the entirety of Earth’s surface.

Figure 2. Landsat 8 Orbit

THF-15 will launch into a parking orbit, where it can initiate an upper stage burn to reach the high inclination of Landsat 8 and wait for the optimal timing. The target location for the intercept is located at the apogee of Landsat 8, when its velocity will be at a minimum. This will reduce the velocity change (ΔV) required to decrease the impact velocity of THF-15.

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C. Satellite-to-Satellite Interface

Before the repair robot is deployed, a secure connection between THF-15 and Landsat 8 must be established. A proximity sensor will detect a successful docking of the satellite and initiate deployment of the robot. The removal and replacement of the TIRS will be programmed for the robot to complete autonomously. This will reduce the amount of data transfer required and eliminate latency errors with video imaging feed that would occur without robot autonomy. Once the repair is complete, the robot will communicate with the ground station to report the success of the mission. Upon successful completion, the ground station will reply with a disengage command and the robot will be retracted.

D. Post-Mission Operations

Once THF-15 has detached from Landsat 8, it will initiate a ΔV maneuver to enter the retirement phase of the satellite. Two possible methods of disposal are dependent on the remaining fuel onboard. The first method requires decreasing the momentum of the satellite until it falls back to Earth, during which it disintegrates upon reentry into the atmosphere. The alternative is to use a Hohmann transfer orbit to reach a super-synchronous (graveyard) orbit. The latter would require significantly more fuel, but also provide the satellite with more orbital capabilities before retirement.

III. Physical Craft

A. Launch Vehicle

THF-15 has two major launch segment requirements that serve as performance drivers for the selection of the launch vehicle. The satellite must carry a payload of greater than 600 kilograms and intercept Landsat 8 on its orbit. As stated earlier, the most reliable strategy for rendezvous missions is using a parking orbit to increase the launch window. During this parking orbit, THF-15 will change its inclination to 98.23˚ to match that of Landsat 8. This maneuver will require the use of an upper stage rocket. In summary, THF-15 will require a launch vehicle with a large payload to orbit capability and two-stage rocket configuration to reach high inclination orbits.

Using these launch requirements, two currently operational rockets were selected for further trade study. Falcon 9 is a two-stage rocket designed by SpaceX with thirteen successful launches to date. The Atlas V 401, a proven launch vehicle of the United Launch Alliance, also has two stages and claims twenty-five successful launches. Table 2 lists key performance characteristics of both vehicles.

Table 2. Launch Vehicle Specifications

Specification Falcon 9 Atlas V 401

Stage 1 Nine Merlin 1D Engines Common Core Booster

Stage 2 Merlin 1C Vacuum Engine Centaur Upper Stage

Payload to SSO 7,348 kg 6,670 kg

Payload Fairing Dimensions

5.2 m Diameter13.1 m Length

4.2 m Diameter12.0 m Length

Comparison of these two rockets based on the above criteria will not lead to a decisive decision. Both rockets have the capability to send THF-15 to sun-synchronous orbit (SSO). At this point in the trade study, reliability becomes the determining factor. Falcon 9 has yet to launch to SSO, while the Atlas V 401

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has completed three successful launches to SSO. One such mission was the launch of Landsat 8, the satellite THF-15 is intercepting.

Based on these findings, THF-15 will use the Atlas V 401 (Fig. 3) launch vehicle to accomplish the primary objective.

Figure 3. Atlas V 401 Configuration

B. Payload

The payload of THF-15 is critical to mission success. It consists of two entities: the repair robot and spare Thermal Infrared Sensor, both developed by NASA and the USGS. Each item has a mass and volume associated with it, and these measurements will affect the design of the bus

The repair robot is an autonomous device that will remove the existing TIRS from Landsat 8 and install the new one. It will deploy after THF-15 establishes a secure connection to Landsat 8. The robot is designed to be send mission data continuously to the ground station until successful completion of the mission is confirmed. Following completion, the robot with retract into the bus of THF-15 and await further command. The mass of the repair robot given by NASA and the USGS is 100 kilograms. The volume is assumed to be 0.5 cubic meters.

The Thermal Infrared Sensor (Fig. 4), one of two sensors utilized by Landsat 8, measures Earth’s surface temperature in two thermal bands. The TIRS uses GaAs Quantum Well Infrared Photodetector arrays, a lower-cost alternative to conventional infrared technology, to detect thermal infrared wavelengths of light.

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Figure 4. Thermal Infrared Sensor (TIRS)

The mass of TIRS is 240 kilograms and occupies 4 cubic meters of space. The estimated dimensions are given as 0.11 x 0.14 x 0.20 meters.

C. Bus

The THF-15 satellite (Figs. 5 & 6) houses the mission payload, propulsion system, and communications structure. This qualifies it as the bus of the mission architecture. Based on the combined volumes of both payload components, THF-15 is projected to have a volume of 5 cubic meters. The dimensions are given as 1.3 x 1.5 x 2.6 meters.

Figure 5. THF-15 Trimetric View Figure 6. THF-15 Front and Side Views

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In order to safely intercept Landsat 8 and attach to the satellite structure, the deployment face of THF-15 must be in the direction of motion. This requires THF-15 to have 3-axis attitude control, with a nadir-facing communications antenna. Due to THF-15’s sun-synchronous orbit, the onboard solar panel will receive constant solar energy to meet the power requirements. The propulsion system, in the form of two pivoting thrusters, provides maneuverability and maintains attitude control. THF-15 also features a reaction wheel that will provide additional attitude control by rotating the satellite by small amounts. This appendage will assure proper alignment of THF-15 and may potentially reduce the amount of fuel needed to complete the mission.

IV. Ground Systems

A. Launch Station

The THF-15 satellite will launch from Vandenberg Air Force Base SLC-3E (Fig. 7), located at 34.6423°N-120.5885°W. The East-West coastline at Vandenberg will allow THF-15 to launch at an over-ocean polar trajectory that will avoid passing landfall until reaching Antarctica. SLC-3E has had thirty-seven launches with the latest being August 13, 2014. The Inclination range is from 51°-145°, which fits our targeted value of 98.23°. As of right now, the Atlas V 401 has a clear range for July 2016. THF-15 will join with GeoEye-2 on its earth imaging mission, which is also aimed for a Sun-synchronous orbit making for a timely and cheaper deployment.

Figure 7. Vandenberg Air Force Base SLC-3E

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B. Mission Operations

The USGS currently utilizes a collection of ground stations called the Landsat Data Continuity Mission (LCDM) Ground System. This system includes all of the ground-based assets required to operate the LDCM program. The three ground stations that compose the Landsat 8 Ground Network (LGN) are located in Sioux Falls, South Dakota; Fairbanks, Alaska; and Svalbard, Norway. The stations downlink mission and telemetry data and uplink commands to the satellite. Since the USGS will already be operating Landsat 8 from these locations, THF-15 will use the existing facilities instead of constructing new ones. Additionally, the USGS is a participant in the Landsat International Cooperator Network (Fig. 8), the benefits of which include global ground station link capabilities.

Figure 8. Landsat International Cooperator Network

C. Command / Control / Communications

Similar to the mission operations segment, THF-15 will take advantage of the existing USGS infrastructure. The most critical CCC requirements focus on the primary objective of THF-15’s mission. Successful completion will require highly-accurate positioning data of both satellites, low latency between THF-15 and mission command, and constant communication between the robot and command during the repair of TIRS. Fig. 9. Displays the data flow of THF-15 during the mission.

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Figure 9. THF-15 Data Flow Diagram

V. Cost

A. Non-Recurring Costs

The non-recurring costs of the THF-15 project are broken down into software development (Table 3), spacecraft development (Table 4), and launch (Table 5). Software development is calculated by estimating forty-thousand source lines of code and using averages for engineer salary and lines written per month.

Table 3. Software Development Cost

Software ValueTotal Lines of Code 40,000

Cost Per Month $16,667Lines Per Month 111

Total Cost $6,006,126.13

Table 4. Spacecraft Development Cost

First Flight Unit CER ($K) Cost Drivers X1 Cost

THF-15 Bus Y = 110.2*X1 X1 = Spacecraft Weight (kg) 800 $88,160,000

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Table 5. Launch Cost

Launch CostULA Atlas V 401 $200,000,000

The total non-recurring cost for the THF-15 project is $294,166,126.13. For practical purposes, this cost will be rounded to $300 million.

B. Recurring Costs

The recurring costs for the THF-15 project are the labor costs that occur over the operational lifespan (Table 6). Again, estimates for staff size and salary are based on averages.

Table 6. Operational Cost

Manpower Number Salary Number of Years CostEngineers 50 $140,000 7 $49,000,000

Technicians 25 $105,000 7 $18,375,000

The total recurring cost per year is $9,625,000. This will result in THF-15 having an overall cost of $361,541,126.

VI. Summary

A. Feasibility

THF-15 will achieve complete mission success. It will launch on the Atlas V 401 rocket, which has proven capability to reach the required orbit and is currently scheduled for July 2016. The satellite will safely transport the spare TIRS and repair robot to Landsat 8 and successfully install the sensor. Finally, THF-15 will disengage from Landsat 8 and enter a parking orbit until retirement, thus completing all mission objectives.

B. Schedule

The estimated operational timeline for the THF-15 project is shown as a Gantt chart representation (Fig. 10).

Figure 10. THF-15 Gantt Chart

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VII. References

A. Atlas V Launch Services User’s Guidehttp://www.ulalaunch.com/uploads/docs/AtlasVUsersGuide2010.pdf

B. Falcon 9 Launch Vehicle Payload User’s Guidehttp://decadal.gsfc.nasa.gov/pace-201206mdl/Launch%20Vehicle%20Information/Falcon9UsersGuide_2009.pdf

C. NASA – Landsat 8http://www.nasa.gov/mission_pages/landsat/main/#.VDznD_ldXyA

D. USGS – Landsat 8http://landsat.usgs.gov/landsat8.php

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